(1) Field of the Invention
The present invention relates to a piloting assistance method, to a piloting assistance device, and to an aircraft having the piloting assistance device.
The invention thus lies in the technical field of instruments for providing assistance in piloting an aircraft, and more particularly a rotorcraft.
(2) Description of Related Art
Document EP 1 598 720 describes a piloting indicator having a calculation unit. The calculation unit displays a symbol on a display screen, the symbol representing a maximum total ground slope for an aircraft, the symbol being superposed on a representation of the relief of the terrain.
It is recalled that the current ground slope of an aircraft represents the angle made by the ground speed vector of said aircraft relative to a horizontal plane, i.e. a plane normal to the direction in which gravity acts. The current ground slope makes it possible to determine the short-term trajectory of the aircraft.
In contrast, the total ground slope of an aircraft serves to predict the long-term trajectory of the aircraft relative to the ground and is a function of the total energy balance of the aircraft. The total ground slope of an aircraft takes account of the instantaneous acceleration on the trajectory of said aircraft.
It should be observed that the term “total air slope” designates the long-term trajectory of the aircraft relative to the mass of air surrounding the aircraft.
Furthermore, aircraft include rotorcraft that are provided with a rotary wing for providing lift, the rotary wing possibly also contributing to propulsion of the rotorcraft.
During a slow descent of a rotorcraft, a dangerous phenomenon referred to as a “vortex state” can appear under certain conditions. This vortex state gives rise to a general loss of lift and maneuverability.
This phenomenon may appear at a vertical air speed of a helicopter that is below a first threshold, and with an air speed in translation that is below a second threshold.
The vortex state is thus dangerous. Nevertheless, a pilot can escape from this vortex state, for example either by beginning to move in translation, or else by increasing the vertical air speed of the aircraft so that the aircraft is no longer in the high-risk flight envelope.
Furthermore, rotorcraft include hybrid aircraft having a rotary wing and also at least one propulsive propeller. The propulsive propeller may generate positive traction, i.e. acting in a direction going from the rear of the aircraft towards the front of the aircraft, or indeed negative traction, i.e. in a direction going from the front of the aircraft towards the rear of the aircraft.
Under such circumstances, the mechanical transmission driving the propeller may be the subject of a limitation, in particular a limitation when the helicopter is exerting negative traction. Such a limitation is referred to as the “negative power limit” for convenience.
This limitation puts a limit on the total ground slope that the aircraft can have in descent.
The following documents are also known: FR 2 783 500 A1, FR 2 887 065 A1, and U.S. Pat. No. 4,004,758 A.